Pyrolytic graphite nose tip for hypervelocity conical reentry vehicles

ABSTRACT

A pyrolytic graphite nose cone tip for hypervelocity conical reentry vehicles in which thermal strain compatibility is achieved longitudinally, radially, and through the load paths of the nose cone tip, by positioning adjoining plates of pyrolytic graphite of varying composition, of varying number, and of varying thickness, along the most forward portion of the nose cone tip; orienting the plates so that they are less thermally conductive in the longitudinal direction (i.e. forward) than they are radially; and, contouring the plates to conform to the desired nose cone tip external configuration.

United States Patent' Inventor Raymond G. Corkery Redlands, Calil.

App]. No. 800.648

Filed Feb. 19. I969 Patented Aug. 3, 1971 Assignee The United States of America as represented by the Secretary of the Air Force PYROLYTIC GRAPHITE NOSE TIP FOR HYPERVELOCITY CONICAL REENTRY VEHICLES 4 Claims, 1 Drawing Fig.

[1.8. CI. l. 102/105, 244/! I7 Int. Cl. F42b 15/00 Field of Search l02/l05; 244/13 S, 1 l7 References Cited OTHER REFERENCES Missile Engineering; Aviation Week & Space Technology; April 8. 1963; New Pyrolytic Graphite Formation Method" pp. 94, 9S 8t 97; 244/l l7.l

Primary Examiner-Robert F. Stahl Anomeys- Harry A. Herbert. Jr. and Arsen Tashjian ABSTRACT: A pyrolytic graphite nose cone tip for hypervelocity conical reentry vehicles in which thermal strain compatibility is achieved longitudinally, radially, and through the load paths of the nose cone tip, by positioning adjoining plates of pyrolytic graphite of varying composition, of varying number, and of varying thickness, along the most forward portion of the nose cone tip; orienting the plates so that they are less thermally conductive in the longitudinal direction (i.e. forward) than they are radially; and, contouring the plates to conform to the desired nose cone tip external configuration.

PAIENIED AUG sum PYROLYTIC GRAPHITE NOSE TIP FOR HYPERVELOCITY CONICAL REEN'IRY VEHICLES BACKGROUND OF THE INVENTION This invention relates to the nose cone of a hypervelocity conical reentry vehicle of the ballistic type, and more particularly, to the nose tip portion thereof.

It is well-known in the art that pyrolytic graphites, and composites thereof, are the leading materials for high-temperature aerospace applications, such as nose cone tips of hypervelocity, conical reentry vehicles (or projectiles) particularly of the ballistic type.

Their popularity and attractiveness is due to but not limited to, their anisotropic thermal properties, mechanical stability at high temperature, low cost, high sublimation temperature, low erosion rate, low density, and good heat radiation characteristics. Unfortunately, pyrolytic graphites fall short of maximum performance characteristics primarily because of the limitations imposed by the conventional method of fabricating curved parts thereof.

That method comprises, essentially, the thermal decomposition of a hydrocarbon gas on a heated female mandrel. In the case of nose cone tips this process results in a thickness"-toradius ratio of approximately lz at the maximum.

By thickness is meant the thickness of the nose cone tip wall and by radius is meant the radius along the line, and in the same plane, as where the measurement of the thickness is taken. in other words, assuming that the nose cone tip is in a longitudinal position and a perpendicular is erected to the longitudinal axis, the length from the point of intersection of the longitudinal axis, and of the perpendicular to the external surface of the nose cone tip wall along the perpendicular, is the "radius." The thickness" is the length along the perpendicular from the external surface of the nose cone tip wall to the internal surface of the nose cone tip wall.

However, for a hypervelocity conical reentry vehicle of the ballistic type, the thickness-toradius" ratio required in the nose cone tip greatly exceeds the 1:20 ratio attainable by the a conventional fabrication method.

Additionally if, by chance, an acceptable if not entirely desirable thickness" -toradius" ratio is attained as to a particular nose cone tip, the nose cone tip wall delaminates (i.e., shears); thickness" is reduced; and the purpose of the buildup of the nose cone tip wall is defeated.

It is to be noted and emphasized that theseproblems are inherent to and are limited to the fabrication of curved parts, such as nose cone tips, when using the conventional fabrication method. These problems, i.e., the inability to attain desired thickness and the undesired delamination and shearing, do thickness" and the undesired delamination and shearing, do not arise in connection with the fabrication of flat parts, such as plates, discs and the like.

My invention eliminates the current problems associated with fabrication of curved parts of pyrolytic graphite, such as nose cone tips; and, thereby, significantly advances the state of the art. l do so, in essence, by providing a method of fabricating a solid, rather than a hollow, forward portion of the pyrolytic graphite nose cone tip and by varying the coinposition of the pyrolytic graphite by using additives.

SUMMARY OF THE INVENTION This invention relates to a hypervelocity ballistic-type conical reentry vehicle nose cone tip, and in addition a method of fabricating same.

Therefore, an object of this invention is to provide a novel hypervelocity ballistic-type conical reentry vehicle nose cone tip.

Obviously, another object of this invention is to provide a nose cone tip which will successful survive the extremely high thermal environmental exposure encountered upon atmospheric reentry.

Still another object is to provide a method of fabricating a nose cone tip, such as described in the foregoing objects.

These and still other similar and related objects of this invention will become readily apparent after a consideration of the description of the invention and reference to the drawing.

DESCRIPTION OF THE DRAWING The drawing is a side elevation view, in longitudinal cross section and in schematic form, partly fragmented, of a preferred embodiment of the invention, showing in phantom the initial configuration.

DESCRIPTION OF A PREFERRED EMBODIMENT With reference to the drawing, therein is shown a longitudinal cross section of a preferred embodiment, with longitudinalaxis E-F, and positions (hereinafter referred to as stations, an art-accepted designation for positions) S, S, and S perpendicular to said longitudinal axis E-F.

Also shown in the drawing, is a typical radius," R, and thickness," T, as defined and explained heretofore. It is to be noted that R and T are shown for prior an illustrative purposes only; that R and T have no applicability, as such to my invention and any embodiment thereof; and that where R and T are in fact positioned in the drawing, the embodiment is solid and there is no thickness," T.

Further with reference to the drawing, therein is shown rod or bolt 11, preferably of a pyrolytic graphite, with threaded flangelike configuration 12 at one end and threaded shank 13 at the other end. A plurality of flatplates, such as 21, 22 and 23, also preferablyv of a pyrolytic graphite, are positioned at, and aft (i.e. rearwardly) of, flangelike end 12 of bolt 11, and are aligned one behind the'other. The flat plates, such as 21, 22 and 23, are oriented so that they have high thermal conductivity in the A-B plane (i.e., radial direction) as indicated in'the drawing, and low therinal conductivity in the C-D plane (i.e., longitudinal direction), as shown. The adjoining surfaces of adjacent plates, suchas 21, 22 and 23, abut and are in close contact with each other, in the manner shown in the drawing.

Aft (rearwardly, i.e. to the reader's right) of the last of the aligned plates, such as23, there ispositioned a cone frustum 31, also preferably of a pyrolytic graphite, which abuts and is in close contact with the most aft plate 23 at tapered end 32 of frustum 31, as shown'in the drawing. The other end 33 of cone frustum 31 is shown fragmented.

Wholly within cone frustum 31, and having thesame slant as cone frustum 31, is cone frustum shaped ballast 41', with aft cavity 42 and centrally located longitudinal cylindrical cavity 43. Cavities 42 and 43 form, at their juncture, a surface 46 essentially parallel to the aft surface of the most rearwardly disposed flat plate 23 of the plurality of aligned adjacent flat plates, such as 21, 22 and 23. Ballast 41 is preferably of a tungsten alloy and is positioned with the tapered end 44 fore (forwardly, i.e. to the reader's left). The aft end 45 of ballast 41 is shown fragmented.

lnterposed between the tapered fore end 44 of ballast 41 and the aft surface of the last or most rearwardly disposed flat plate 23 is washer 51, also preferably of a pyrolytic graphite, although it could be of a porous graphite. Washer 51 has an opening of the same diameter as the diameter of ballast longitudinal cylindrical cavity 43, with the opening of each registering.

Ballast 41 and washer 51 are affixed to, and are made integral to, cone frustum 31 by a suitable bond 61.

Still with reference to the drawing, disposed between bolt 11, and ballast 41 with washer 51, is open-ended longitudinal circular cylinder 71, also of a pyrolytic graphite, although it could be of a porous graphite.

Disposed over shank 13 of bolt, and with its footing resting on the internal lateral surface 46 of cavity 42 of ballast 41, is belleville type spring". Also disposed over shank 13, and amp of spring 81, is washer 82, also of a pyrolytic graphite, although it could be of a' porous graphite. Screwed onto the threaded portion of shank 13, and abutting washer 82, is pyrolytic graphite nut 83, which also could be of a porous graphite.

It is to be understood that whenever and wherever applicant has made and makes reference to a pyrolytic graphite," a Z series grade of pyrolytic graphite (such as ZTA," which is available commercially from the National Carbon Company, 270 Park Avenue, New York l7, New York), rather than a standard grade ATJ" graphite, is preferred. In addition and with specific reference to the flat plates, such as 21, 22 and 23, it is to be understood that the pyrolytic graphite of which they are made is not only of 2" series grade, but also preferably has titanium, hafnium, or boron as an additive.

METHOD OF FABRICATlON AND MODE OF OPERATION OF THE PREFERRED EMBODIMENT A member 11 of a pyrolytic graphite is contoured or shaped, by suitable means, to the desired configuration, with a flangelike terminus 12 at one end and a shank 13 at the other end. The preferred configuration of member 11 is, in this instance, that of a cylindrical step-down-type bolt. Ends 12 and 13 are then threaded. The first (i.e. most forwardly disposed), pyrolytic graphite flat plate 21 is reamed, threaded to mate with, and is screwed onto flangelike threaded end 12 of bolt 1 1 with the cross-grain oriented normal to longitudinal axis E-F, which is also the spin axis. A %-16 standard thread 0.2 inch deep is preferred. More aft subsequent flat plates, such as 22 and 23, are each reamed or the like to fonn an opening of the same configuration as member 11 and, in this instance, the opening would be circular and 0.4 inch in diameter. These more aft subsequent flat plates, such as 22 and 23, are then fitted over shank 13, pushed toward end 12, and the adjoining surfaces of adjacent plates are made to abut and to be in close contact with each other are also oriented with the cross-grain normal to spin axis E-F. Additionally, all plates, such as 21, 22 and 23, are oriented so that they are more thermally conductive in the A-B plane (i.e. radial direction) than they are thermally conductive-in the C-D plane (i.e. the longitudinal direction).

The shank end 13 of bolt 11 is then passed through the opening provided by the longitudinal open-ended circular cylinder 71 and the aft end of the preferred embodiment, which includes cone frustum 31, ballast 41, and washer 51. The wall of cylinder 71 is preferably 0.1 inch thick and its purpose'is to thermally isolate bolt 11 from ballast 41. Washer 51 is preferably 0.125 inch thick and its purposeis to thermally protect tapered end 44 (i.e. the forward face of ballast 41). Ballast 41 is preferably of a tungsten alloy.

Belleville type spring 81 is then passed over shank end 13; washer 82 is also passed over shank 13; and nut 83 is screwed onto shank 13 until it abuts washer 82, compresses spring 81, places bolt 11 under longitudinal tension, and rigidly secures bolt 11, with plates 21, 22 and 23 thereon, to the aft portion of the nose cone tip. Spring 81 has the capability of deflecting 0. l 25 inch and is insulated from bolt 11 by washer 82.

The flat plates, such as 21, 22 and 23, are then contoured by suitable means, such as machining, to conform to the desired external configuration which, in this instance, is a three-eights nose tip radius and 8.6 half-angle. With reference to the drawing, the portion shown in phantom therein is removed, leaving and resulting in, a nose cone tip which is solid from station S to station 5,.

Applicant's explanation of the phenomena involved is as follows:

The major considerations are the thermal strain compatibility in both the longitudinal and the radial directions and the load paths through the nose cone tip. With reference to the drawing, from station S to station 8,, the radial thermal strain compatibility is obtained by the inherent properties of 2" grade series pyrolytic graphite bolt 11 and the A-B direction high thermal conductivity of plates 21, 22 and 23. However, there is an incompatibility in the longitudinal direction with the C-D plane direction of plates 21, 22 and 23. This is alleviated by compressing belleville-type spring 81 underZ" series grade pyrolytic graphite nut 83. From station 5: to station S;, the radial thermal strain compatibility is obtained by controlling the heat leak into tungsten alloy ballast 41 through pyrolytic graphite open-ended cylinder 71 around bolt 11.

Due to the low structural properties of the C-D plane direction, all the bending and shear loads will be taken in bolt 1 1 to station S The preload on nut 83 will prevent opening a gap at station 8;. The shear and bending increment at station 5 will be introduced into ballast 41 by a redundant load path,

the first as a socket (i.e. longitudinal cavity 43) between station S and station 5;, and the second as compression on ballast 41 and tension in bolt 11.

While there has been shown and described the fundamenta features of my invention, as applied to a preferred and particular embodiment, it is to be understood that this is by way of illustration only and is not intended as a limitation, and that various substitutions and omissions may be made by those skilled in the art without departing from the spirit of the invention. For example, the plates may be varied as to number, thickness and composition. As to the variation in composition, a titanium or hafnium pyrolytic graphite composition may be used may be used for minimum shape change, and a boron pyrolytic graphite may be used for thermal conductivity control.

What 1 claim is:

1. The most forward portion of a nose cone tip for a hypervelocity conical ballistic-type reentry vehicle, comprising:

a. a boltlike member of a pyrolytic graphite, the length of which is substantially greater than its width, with said boltlike member having a forwardly disposed end and a rearwardly disposed end;

b. a plurality of flat plates of a pyrolytic graphite, aligned one behind the other, with adjoining surfaces of adjacent plates being in close contact with each other, and with each said flat plate having an opening to accept, fit on and along, the length of said boltlike member, and with each said flat plate oriented to be more thermally conductive in the direction of the width of said boltlike length of said boltlike member, and with all said flat plates positioned at the forwardly disposed end of said boltlike member;

. means for attaching the most forwardly located flat plate of said plurality of aligned flat plates to the forwardly disposed end of said boltlike member;

d. means for maintaining all flat plates, of said plurality of flat plates, under pressure, along the length of said boltlike member and in the direction of the forwardly disposed end of said boltlike member,

e. and, means for contouring the external surface of all flat plates, of said plurality of flat plates, to conform to the desired configuration.

2. The most forward portion of the nose cone tip, as set forth in claim 1, wherein said means for attaching the most forwardly located flat plate, of said plurality of aligned flat plates, to the forwardly disposed end of said boltlike member includes:

a. threads on the forwardly disposed end of said boltlike member;

b. and, mating threads along the inner periphery of the opening in the most forwardly located plate-of said plurality of aligned flat plates with said threaded, most forwardly located, plate being screwed onto said threaded, forwardly disposed, end of said boltlike member.

3. The most forward portion of the nose cone tip as set forth in claim 2, wherein said means for maintaining all flat plates, of said plurality of flat plates, under pressure, along the length of said boltlike member and in the direction of the forwardly disposed end of said boltlike member includes:

a. the rearwardly disposed end of said boltlike member, with said end having a shank configuration and being threaded;

the aft portion of the nose cone tip, having a cone frustum configuration with the tapered end forward, with said aft portion being solid and having a centrally located longitudinal cavity running from the tapered end to an aft cavity, with the cavities forming at their juncture a surface essentially parallel to the aft surface of the most rearwardly disposed of the said plurality of aligned flat plates;

. a belleville type spring positioned over the threaded to mate with the threads on the threaded shank of the rearwardly disposed end of said boltlike member with said nut screwed onto the threaded shank of the rearwardly disposed end of said boltlike member.

4. The aft section of the nose cone tip, as set forthin claim 3, having:

'a. an external surface of pyrolytic graphite;

b. a cone frustum shaped ballast of a tungsten alloy, wholly internal of said external surface, with said ballast being positioned with the tapered end forward and having therein said centrally located longitudinal cavity and said aft cavity;

c. a washer of pyrolytic graphite disposed between the tapered end of said ballast and the most rearwardly disposed flat plate of said plurality of aligned flat plates;

d. means for bonding said external surface to said ballast and washer, to form an integral unit;

e. and, an open-ended longitudinal circular cylinder of a pyrolytic graphite wholly within. and the same length as, said longitudinal cavity, with the external surface of said cylinder abutting the internal surface of said longitudinal cavity. 

2. The most forward portion of the nose cone tip, as set forth in claim 1, wherein said means for attaching the most forwardly located flat plate, of said plurality of aligned flat plates, to the forwardly disposed end of said boltlike member includes: a. threads on the forwardly disposed end of said boltlike member; b. and, mating threads along the inner periphery of the opening in the most forwardly located plate of said plurality of aligned flat plates with said threaded, most forwardly located, plate being screwed onto said threaded, forwardly disposed, end of said boltlike member.
 3. The most forward portion of the nose cone tip as set forth in claim 2, wherein said means for maintaining all flat plates, of said plurality of flat plates, under pressure, along the length of said boltlike member and in the direction of the forwardly disposed end of said boltlike member includes: a. the rearwardly disposed end of said boltlike member, with said end having a shank configuration and being threaded; b. the aft portion of the nose cone tip, having a cone frustum configuration with the tapered end forward, with said aft portion being solid and having a centrally located longitudinal cavity running from the tapered end to an aft cavity, with the cavities forming at their juncture a surface essentially parallel to the aft surface of the most rearwardly disposed of the said plurality of aligned flat plates; c. a belleville type spring positioned over the threaded shank of the rearwardly disposed end of said boltlike member, with said spring resting on the surface formed at the juncture of the longitudinal cavity and aft cavity of the said aft portion of the nose cone tip; d. a washer of a pyrolytic graphite positioned over the threaded shank of the rearwardly disposed end of said boltlike member, with said washer abutting on, and located atop of, said belleville type spring; e. and, a nut of ''''Z'''' series grade pyrolytic graphite threaded to mate with the threads on the threaded shank of the rearwardly disposed end of said boltlike member with said nut screwed onto the threaded shank of the rearwardly disposed end of said boltlike member.
 4. The aft section of the nose cone tip, as set forth in claim 3, having: a. an external surface of pyrolytic graphite; b. a cone frustum shaped ballast of a tungsten alloy, wholly internal of said external surface, with said ballast being positioned with the tapered end forward and having therein said centrally located longitudinal cavity and said aft cavity; c. a washer of pyrolytic graphite disposed between the tapered end of said ballast and the most rearwardly disposed flat plate of said plurality of aligned flat plates; d. means for bonding said external surface to said ballast and washer, to form an integral unit; e. and, an open-ended longitudinal circular cylinder of a pyrolytic graphite wholly within, and the same length as, said longitudinal cavity, with the external surface of said cylinder abutting the internal surface of said longitudinal cavity. 